Method for the manufacturing of luminescent screen



P. DELRIEU 2,828,216

March 25, 1958 METHOD FQR THE MANUFACTURING OF LUMINESCENT SCREEN Filed April 18, 1955 A33 Ev\ Fig.2.

Arra w ivmrrion non ran MANUFACTURING or LUMINESCENT SCREEN Pierre Delrieu, Paris, France Application April 18, 1955, Serial No. 502,134

Claims priority, application France April 27, 1954 6 (Jiaims. (Cl. 117-18) This invention relates to a process for providing a supvided with the screen with such suspension, to empty the apparatus and finally to dry thesuspension film remaining on the wall of the apparatus and to bake said film so as to eliminate the solvent in the binder and also the binder itself if it is not intended to remain inside the apparatus.

The binder solutions in which the phosphor may be placed in suspension have a deleterious effect on some phosphors, either because of the temperature and of the oxidizing atmosphere necessary for their elimination or because of the substances evolved by said binders or their solvents when they are heated for expelling them or drying them or again when removing gases from the luminescent layer and its support. The binders with which an adhesive layer is formed which is then dusted with phosphor, olfer,

on the other hand, the drawback of being able to secure only a thin layer of luminescent powder which can absorb only part of the radiation falling thereon. A thicker layer is lacking in adherence and is partly peeled off its support under the action of the shocks which occur during subsequent manufacturing operations, during the placing in position of the apparatus incorporating the luminescent screen, and during the utilization of such apparatus.

I have found that these disadvantages may be overcome by impregnating, at least superficially, the layer of luminescent material with a second amount of hinder, the binder of said second amount being in a liquid state. This method makes it possible to obtain arelatively thick layer of phosphor attached on a support by a binder which causes no deterioration of the phosphor layer.

Preferably, a single liquid is used for impregnating the luminescent layer, already secured, with the second amount of binder, the binder being in a free condition or in a combined condition. This liquid is, forins'tance, a solution of this second amount, a solution in which the binder is in a combined condition or not. An aqueous solution may be used, for instance, of potassium silicate, already used for coating the support with the first amount of hinder, or else a liquid obtained by dissolving boric anhydride or boric acid in methyl alcohol. In the latter case; the binder, i. e. boric anhydride,'is perhaps, at least in part in the condition of methyl borate in the liquid.

The use of this second amount of binder makes it possible to obtain a luminescent layer relatively thick and oflering, however, quite a satisfactory adherence to its support. The binder cements the grains located far from the first layer of binder with those which are near it and inaddition, the lubrication by the liquid and its surface States Patent tension probably allow the grains of the layer of powder to gather together, forming a more compact layer.

It is also possible, over a first luminescent layer, thin or thick, thus impregnated with liquid, to spread by dusting a second luminescent layer. If necessary, other luminescent layers may be added, each one of the layers to be coated being impregnated with binder previous to such coating.

In order that the said invention may be clearly understood and readily carried into efiect the same will be described hereinafter with reference to the accompanying drawings, wherein:

Figure 1 represents a transverse section of a portion of a screen, with a single luminescent layer.

Figure 2 represents a transverse section of a portion of another screen, comprising two luminescent layers.

Figure 3 represents a device used for impregnating a luminescent layer with a second amount of binder.

Figure 1 represents, in transverse section, a fragment of a glass balloon flask 1, coated internally with a single, thick, layer 3 of fluorescent material. The balloon flask which is intended to form an additional envelope for a mercury vapour lamp, decreases the effect of atmospheric conditions on the temperature of such a lamp and, by virtue of its fluorescent layer 3, it transforms the ultra violet radiation of the lamp into a red light which completes, to a certain extent, the blue-green light emitted by said lamp. The assembly ofthe lamp and balloon flask constitutes what is called a mercury vapour lamp with corrected light.

For the purposes of illustration, the various layers shown in Figures 1 and 2 are represented therein by continuous and parallel lines. Actually, the separating surfaces are very irregular, except for the walls of the balloon flask as the grains of luminescent powder partly enter the viscous binder layer on which they are deposited.

The deposition of the layer 3 is elfected by the following method: Into the balloon flask 1, a certain amount of an aqueous solution of potassium silicate is introduced and the flask is then inclined and rotated so as to wet its entire inner wall with said solution, whereafter it is turned upside down so that the solution in excess can drip off. The film 2 which remains adherent to the wall is then possibly partly dried off by leaving the flask open. This film contains the first amount of binder. A certain amount of fluorescent powder is then projected over the film 2, for instance by means of an air stream. These operations are known and carried out industrially, with the exception that heretofore the amount of powder which was deposited was smaller so as to avoid the possibility of subsequent peeling or displacement of the layer 3.

In the present instance, in order that the luminescent layer3 may be thicker, but offer no risk of peeling off locally from its support 1, a further operation is carried out. This further operation consists in impregnating the layer 3 with a second amount of binder, which is in a liquid condition so that it may flow and then subsequently transforming said binder to a solid state.

This binder which comprises, for example, potassium silicate, is made liquid by dissolution in water and is thereafter transformed into a solid by evaporating the water. The binder may also comprise boric anhydride, made liquid by the addition of methyl alcohol with a portion of which it may possibly combine to form methyl borate which is dissolved by the remainder of the alcohol.

Instead of boric anhydride, boric acid may also be employed if the water present in the latter offers no drawback, for instance that of deteriorating the phosphor. The boric anhydride, which will serve as a binder, is

regenerated by evaporation and drying under a vacuum if necessary. This regeneration probably involves the Patented Mar. 25, 1958,

following process: evaporation of the alcohol; decomposition of methyl borate, giving methyl alcohol, which evaporates, and boric acid; decomposition of the boric acid into Water, which evaporates, and boric anhydride.

The hardening of certain binders may not be accompanied by the elimination of substances which have been mixed with these binders for making them liquid. One may, for example, either spray over the layer 3 a molten binder which will harden'upon cooling or alternatively impregnate such layer with a binder in a slightly polymerized condition, which will be further polymerized and hardened by heating.

These methods give a fluorescent layer 3, the grains of which are cemented together by the second amount of binder and the adhesion of which to the inner wall of the flask It is ensured by the first amount of binder forming the layer 2.

The layer of fluorescent material and the second amount of binder are represented only in the figure, by a single layer, 3, since the binder impregnates this material without forming any substantial excess thickness at its surface provided of course that too much of it has not been deposited.

It is not necessary to impregnate the luminescent grains closest to the layer 2, as these grains are already strongly glued by the first amount of binder.

Figure 2 also represents a fragment of a balloon flask 1, which is to be incorporated in a mercury vapour lamp with corrected light, and the various layers deposited on the inner surface of said flask. These layers comprise, as in the case of Figure 1,'a layer of binder 2 and a layer 3 of fluorescent powder cemented by a second amount of binder. In the embodiment shown in Figure 2 however there is, in addition, an additional layer 5 of fluorescent material.

For obtaining these various layers and giving them a satisfactory adherence, the process above described in connection with Figure 1, is carried out except that the step of hardening the second amount of binder is omitted. On the layer 3 made tacky by the second application of binder still in a liquid condition, powdered phosphor is I projected in the manner indicated for the layer 3. The amount of this material which adheres fairly strongly to the layer 3 constitutes the layer 5 and subsequently to the application of such layer hardening of the;second amount of binder is effected.

This process of distribution of the fluorescent powder into several successive layers is particularly suitable in cases where itis desired to obtain a very uniform deposit. The projection .of substantial amounts of fluorescent powder' for obtaining a thick deposit, often leads to local excessive thicknesseswhich "do not result with thin deposits.

This process also makes it possible to .fix a larger amount of fluorescent powder than the one layer process.

The assembly of the layers 3 and 5 adheres strongly to the wall 1 and may offer a thickness very definitely larger than that of a single layer 3 which would not have been cemented by the second amount of binder. Such an assembly allows a more complete utilization of the ultra violet radiation.

Figure 3 shows a device used for impregnating, with the second amount of binder, a luminescent layer 3 deposited on the inner wall of a flask 1.

A burette 7 contains the second binder 8 in a liquid condition, for example a solution of boric acid in methyl alcohol. This burette carries graduation marks 9, 10, which are for example so disposed that the volume contained between two successive marks will be sufiicient for one impregnation. A tube 12 with a cock 11 extends from the bottom of the burette 7 and projects into the neck 14 of the flask. By opening the cock 11, the opersimply flowing along the line of maximum slope, binder spreads due to capillarity and by rotating the flask about its axis as indicated by the arrow 15, the binder is made toimpregnate the layer 3 entirely and in a substantially uniform manner before an excess of liquid appears at the lowest point in the flask; draining is then effected, preferably after adding yet a further small amount of binder.

The principle of the device shown in Figure 3 may be applied to an automatic machine. It is possible also to use a device which will spray the binder in a liquid state, either by pressure or by a gas stream which induces a suction effect, but the impact of the sprayed liquid may detach part of the luminescent material 3.

The following amounts may be used for coating with barium, strontium, lithium silicate, activated by cerium and manganese, the inside of a glass balloon flask 1 having an inside diameter of mm., such a flask being intended to serve as a fluorescent envelope for a high pressure 125 watts mercury vapour lamp:

For the first layer of binder, 300 cm. of a solution of potassium silicate in distilled water is employed. Out of this amount,0.2 to 0.7 cm. will remain on the glass after the excess liquid has been removed by draining and partial evaporation, andwill form a film on which the fluorescent powder will be deposited by projection If it is desired to form a single layer 3 of luminescent material then, 1.5 to 2.5 g. of the above triple silicate are deposited inside the flask. This amount forms a layer which is cemented with 5 cm. of a solution of 10 g. of boric anhydride in g. of methyl alcohol, using the device shown in Figure 3. The amounts of binder are then dried by evaporation and, if necessary, by heating in the open air or under a partial vacuum.

If it is desired to provide two layers of phosphor cemented together and with the first amount of binder by the second amount of binder, then, for the first layer 3, for example, 1.2 g. of triple silicate will be deposited, drying being subsequently effected in an oven. This first layer is then impregnated by the same aqueous soluthe tion of potassium silicate as that used for the first amount of binder whereafter draining is effected and partial drying, but more binder, for example that of 3 cm? of solution, Will remain.

Over the first layer of triple silicate, made tacky by this second, amount of binder, approximately 0.8 g. of the same triple silicate is projected whereafter the binders are dried in anoven, at about 100 C. The total amount ofphosphor deposited and attached is substantially the same as in the case of the one layer process, but the coating is much more uniform.

Byway ofeomparison, on the inner surfaceof the same balloon flask, made tacky by the same solution of potassium silicate, only about 1 g. of the above triple silicate could be-deposited if a satisfactory adhesion is to be obtained,'without however using an additional binder.

On the contrary, the two above methods make it possible to coat the flask with 1.5 to 3 g. of this triple silicate While preserving'also a good adhesion. These processes for example with phosphoric-acid, and with luminescent material other than the triple barium, strontium, lithium silicate activated with cerium and'manganese. It may be used for superposing layers of phosphorsdifferent from one another; and alsoforsuperposin'g more than two layers. Preferably, the binderof the second amount is used in; solution in a volatile liquid, for example acetone inthe-caseof phosphoric acid. r I I What I claim is: p

'1. A process for providing a support surface witli a luminescent screen-,Hsaid support surface having anout 5 wardly projecting portion, comprising, coating said surface with a layer of a first amount of binder, depositing on said layer a layer of luminescent material, said material being in the form of dry powder, and thereafter slowly pouring a second amount of binder on said outwardly projecting portion of said support surface, which portion will be devoid of said layer of luminescent material when the device comprising the screen will be completed, and rotating said support surface; the binder of said second amount being in a liquid state and spreading through the layer of luminescent material by capillary attraction without flowing on the surface of said layer.

2. A process as set forth in claim 1, wherein said second amount of binder consists in potassium silicate dissolved in water.

3. A process as set forth in claim 1, wherein said sec- 6 ond amount of binder consists in phosphoric acid dissolved in water.

4. A. process as set forth in claim 1, wherein said second amount of binder consists in phosphoric acid dissolved in acetone.

5. A process as set forth in claim 1, wherein said second amount of binder consists in boric anhydride dissolved in methyl alcohol.

6. A process as set forth in claim 1, wherein said secondamount of binder consists in boric acid dissolved in methyl alcohol.

Dawihl et a1. Oct. 31, 1939 Fonda Feb. 3, 1948 

1. A PROCESS FOR PROVIDING A SUPPORT SURFACE WITH A LUMINESCENT SCREEN, SAID SUPPORT SURFACE HAVING AN OUTWARDLY PROJECTING PORTION, COMPRISING, COATING SAID SURFACE WITH A LAYER OF A FIRST AMOUNT OF BINDER, DEPOSITING ON SAID LAYER A LAYER OF LUMINESCENT MATERIAL, SAID MATERIAL BEING IN THE FORM OF DRY POWDER, AND THEREAFTER SLOWLY POURING A SECOND AMOUNT OF BINDER ON SAID OUTWARDLY PROJECTING PORTION OF SAID SUPPORT SURFACE, WHICH PORTION WILL BE DEVOID OF SAID LAYER OF LUMINESCENT MATERIAL WHEN THE DEVICE COMPRISING THE SCREEN WILL BE COMPLETED, AND ROTATING SAID SUPPORT SURFACE; THE BINDER OF SAID SECOND AMOUNT BEING IN A LIQUID STATE AND SPREADING THROUGH THE LAYER OF LUMINESCENT MATERIAL BY CAPILLARY ATTRACTION WITHOUT FLOWING ON THE SURFACE OF SAID LAYER. 